This thesis deals with modeling, simulation and operating limits of high-voltage direct-current (HVDC) transmission systems that employ voltage-source converters (VSCs) as their building blocks. This scheme is commonly known as the VSC-HVDC transmission. A simulation-based study is undertaken in which detailed electromagnetic transient (EMT) models are developed for a back-to-back VSC-HVDC transmission system. Different control strategies are implemented and their dynamic performances are investigated in the PSCAD/EMTDC EMT simulator. The research presented in this thesis firstly specifies the factors that limit the operating points of a VSC-HVDC system with particular emphasis on the strength of the terminating ac system. Although the EMT model shows these limits it provides little analytical reason for their presence and extent. A phasor-based quasi-steady state model of the system including the phase-locked loop firing control mechanism is proposed to determine and characterize the factors contributing to these operating limits. Stability margins and limits on the maximum available power are calculated, taking into consideration the maximum voltage rating of the VSC. The variations of ac system short-circuit ratio (SCR) and transformer impedance are proven to significantly impact the operating limits of the VSC-HVDC system. The results show how the power transfer capability reduces as the SCR decreases. The analysis shows that VSC-HVDC converters can operate into much weaker networks, and with less sensitivity, than the conventional line commutated converters (LCC-HVDC). Also for a given SCR the VSC-HVDC system has a significantly larger maximum available power in comparison with LCC-HVDC. A second research thrust of the thesis is introduction of a simplified converter model to reduce the computational intensity of its simulation. This is associated with the admittance matrix inversions required to simulate high-frequency switching of the converter valves. This simplified model is based on the concept of dynamic average-value modelling and provides the ability to generate either the full spectrum or the fundamental-frequency component of the VSC voltage. The model is validated against the detailed VSC-HVDC circuit and shows accurate matching during steady state and transient operation. Major reductions of 50-70% in CPU-time in repetitive simulation studies such as multiple runs and optimization-based controller tuning are achieved.

Thesis (M.App.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 182-190). Also available in electronic format on the Internet.

Thesis (doctoral)--Universität Köln.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 66-73). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 66-73). Also available on the Internet.

Thesis (Ph. D.)--University of California, San Diego, 2005. / Vita. Includes bibliographical references (leaves 248-269).

Thesis (M.S.)--University of Wisconsin--Madison, 1960. / Typescript. eContent provider-neutral record in process. Description based on print version record.

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2006. / Includes bibliographical references (p. 89-91).

A presente pesquisa destina-se a estudar os incentivos tributários. Espécie de norma tributária indutora, os incentivos tributários ainda não receberam a atenção devida por parte dos estudiosos do direito tributário. Atento ao volume cada vez maior de recursos envolvendo incentivos tributários, assim como a necessidade de se conferir maior transparência e responsabilidade na gestão do gasto público, esse trabalho dedica-se a estudar essa ainda pouco explorada figura, extremando-a de figuras parecidas, com as quais não raras vezes é confundida. Embora não haja uma conceituação constitucional ou legal expressa, é possível afirmar que os incentivos tributários são hipóteses de desoneração tributária, que importam em derrogações às regras gerais de tributação, com o não ingresso de recursos nos cofres públicos, de forma a estimular condutas dos contribuintes, com a finalidade de se atingir fins e objetivos constitucionais. Em virtude de sua natureza híbrida, os incentivos tributários se sujeitam a limitações constitucionais tributárias e econômicas, assim como às limitações orçamentário-financeiras. O principal instrumento de compatibilização entre os incentivos tributários, capacidade contributiva, isonomia e cânones da ordem econômica é o princípio da proporcionalidade. Poder Legislativo, Tribunal de Contas e Poder Judiciário devem fiscalizar e controlar essa espécie de desoneração tributária. O Controle a cargo Poder Legislativo (no âmbito do Poder Legislativo federal) tem deixado muito a desejar, tanto no que concerne ao controle dos limites orçamentário-financeiros, quanto no que diz respeito ao controle dos limites constitucionais tributários e econômicos. O Controle que cabe ao Tribunal de Contas (foi analisado o Tribunal de Contas da União) tem mostrado alguma evolução. Contudo, a análise de alguns julgados do TCU demonstra que há muito a melhorar, especialmente no que concerne à investigação da legitimidade e economicidade. A LRF ostenta caráter de norma geral no que tange aos requisitos para a concessão de incentivos tributários. Eventual descumprimento desses preceitos por leis locais revela verdadeira inconstitucionalidade, passível de controle pelo Poder Judiciário. A atuação do Poder Judiciário, em especial do STF, no controle dos incentivos tributários tem sido bastante tímida e pouco transparente. Na maior parte dos casos, o STF tem se limitado a reafirmar o caráter discricionário dos atos oriundos do Poder Legislativo e Executivo, negando-se a examiná-los. Os pedidos de extensão de incentivos tributários também não tem obtido sucesso, pois o STF faz aplicação irrestrita da cláusula do legislador negativo. Uma solução conciliadora seria o judiciário se valer da declaração de inconstitucionalidade sem a pronúncia de nulidade, permitindo a extensão dos incentivos tributários àqueles casos em que a ilegalidade não reside no incentivo em si mesmo, mas na sua não aplicação aos contribuintes em mesma situação. Muito embora existam limites bem definidos, é possível afirmar que o controle dos incentivos tributários precisa evoluir muito. / This research aims to study the tax incentives. Sort of inducer tax rule, the tax incentives have not already received the correct attention by tax law scholars. Keeping an eye on the increase of resources involving the tax incentives, and realizing the necessity of bringing more transparency and responsibility in the management of public expenditure, this work intend to study this little explored figure, distinguishing from other similar figures, which has been many times confused with. Although there has not been a constitutional or legal expressed meaning, it is possible to affirm the tax incentives are kinds of tax exemption, which implies derogation from general rules for taxation, with the not entering of resources into public purse, in order to get constitutional purposes and objectives. Due to this hybrid nature, the tax incentives are subject to constitutional and economic limitations, as well as budget and financial limitation. The main instrument of compatibility between the tax incentives, the ability to pay, equality and the economic order canons is the principle of proportionality. Legislative Power, Court of Auditors and Judiciary must supervise and control this kind of tax exemption. The control made by the Legislative (within the federal scope) has much been lacking, both in terms of controlling the budget and financial limits, and in terms of controlling the constitutional tributary and economic limits. The control by Court of Auditors (the Court of Auditors of Union was analyzed) seems to have some evolution. However the analysis of some Courts judgments reveals that it has much to improve, mainly concerning the investigation of legitimacy and economy. The LRF shows character of general rule in terms of requirement for granting tax incentives. Eventual non-compliance of this precepts by local rules reveals true unconstitutionality, which can be controlled by Judiciary. The actions of the Judicial Power, especially the STF actions, upon the tax incentives control have been fairly timid and lacking in transparency. In many cases, the STF has been limited to the reaffirmation of discretionary character of the acts performed by Legislative and Executive powers, but refusing the analysis of them. The requests of tax incentive extension have been unsuccessful, because of the large unrestricted application of negative legislator clause by STF. A conciliatory solution would be the Judiciary using the declaration of unconstitutionality without nullity pronunciation, allowing the tax incentives extension to that cases which the illegality is not in the incentive itself, but in the act of not applying the incentive extension to the taxpayers who are in the same situation. Although there are clear limits, it is possible to affirm that the tax incentives control still needs to evolve.